1. Field of the Invention
The present invention relates to an underlay substrate, and a screen printing method and a manufacturing method of a printed circuit substrate using the same.
2. Description of the Background Art
As a technique for forming a conductive layer, an insulating layer or the like on a substrate, a screen printing is known. In the screen printing, printing ink (conductive paste, insulating paste or the like) is applied on the substrate through a screen plate in which an opening having a predetermined shape is formed while the substrate is fixed on a stage of a screen printing device. Thus, the conductive layer, the insulating layer or the like whose shape corresponds to the shape of the opening of the screen plate is formed on the substrate.
When the screen printing is performed, the substrate is fixed on the stage by, for example, vacuum suction (see JP 1-115272 U, for example).
When the substrate has an asymmetric shape, the substrate may not be sucked onto the stage with a good balance in the vacuum suction of the substrate onto the stage. Specific description is made using FIG. 6.
FIG. 6 is a diagram showing an example of a substrate sheet subjected to the screen printing. As shown in FIG. 6, a plurality of (two in FIG. 6) substrate assembly regions R1 are provided on the substrate sheet 10 so as to extend in parallel with a pair of sides that face each other.
A plurality of substrate formation regions R2 are provided in each of the substrate assembly regions R1. Hereinafter, the above-mentioned pair of sides of the substrate sheet 10 is referred to as lateral sides, and the other pair of sides that is vertical to the lateral sides is referred to as end sides.
Each of the substrate formation regions R2 is subjected to various types of processes, thereby forming printed circuit substrates. In the example shown in FIG. 6, the printed circuit substrates are magnetic head suspension substrates. Openings R3 are formed at portions excluding the plurality of substrate formation regions R2 in each of the substrate assembly regions R1. Ends of each of the substrate formation regions R2 are coupled to a peripheral region of the substrate assembly region R1.
A blank region R10 is formed in a region excluding the substrate assembly regions R1 in the substrate sheet 10. In the blank region R10, end blank regions R4 are provided so as to extend from respective one ends of the substrate assembly regions R1 to one end side of the substrate sheet 10. In addition, end blank regions R5 are provided so as to extend from the respective other ends of the substrate assembly regions R1 to the other end side of the substrate sheet 10 in the blank region R10. Normally, the end blank regions R4, R5 are formed such that their respective areas are different from each other. Therefore, a region on one side of the blank region R10 and a region on the other side of the blank region R10 have different areas from each other with a center line CL1 passing through the respective centers of the both lateral sides of the substrate sheet 10 as its boundary.
In the vacuum suction of the substrate sheet 10 onto the stage, the suction force is proportional to a contact area between the substrate sheet 10 and the stage. In this substrate sheet 10, the suction force onto the stage is different in the region on the one side and the region on the other side with the center line CL1 as its boundary. Therefore, the substrate sheet 10 is not sucked onto the stage with the good balance.
After the printing ink is applied onto the substrate sheet 10, the stage is lowered, so that the substrate sheet 10 is separated from the screen plate. Here, if the substrate sheet 10 is not sucked onto the stage with the good balance, the following problems are prone to occur.
FIG. 7 is a diagram for explaining the problems in the conventional screen printing. As shown in FIG. 7, viscosity of the printing ink causes a part of the substrate sheet 10 to remain adhered to the screen plate, thereby moving the part of the substrate sheet 10 away from the stage in some cases. In such a case, the substrate sheet 10 is liable to be folded, thereby causing the substrate sheet 10 or the conductive layer or the like on the substrate sheet 10 to be damaged.